Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $55.39   13.649%   $62.9502   $62.95   $62.95   $63.00  
  Purchase #2 $54.91   6.622%   $58.5461   $58.55   $58.55   $58.50  
  Purchase #3 $233.25   4.467%   $243.6693   $243.67   $243.65   $243.70  
  Purchase #4 $17.46   8.563%   $18.9551   $18.96   $18.95   $19.00  
  Purchase #5 $19.55   10.626%   $21.6274   $21.63   $21.65   $21.60  
  Purchase #6 $90.46   4.828%   $94.8274   $94.83   $94.85   $94.80  
  Purchase #7 $45.51   6.396%   $48.4208   $48.42   $48.40   $48.40  
  7 purchase totals = $516.53       $548.9963   $549.01   $549.00   $549.00